The present disclosure relates to a diffractive optical element in which two optical members are stacked, and a diffraction grating is formed at an interface between the two optical members; and to an optical device including the diffractive optical element.
A diffractive optical element has been known, in which a plurality of optical members are stacked, and a relief pattern is formed at an interface between the optical members.
In a diffractive optical element described in, e.g., Japanese Patent Publication No. 09-127321, a relatively low-refractive high-dispersive optical material, and a relatively high-refractive low-dispersive optical material are stacked, and a diffraction grating having a saw-tooth cross-sectional shape is formed at an interface between the optical materials. More specifically, the diffractive optical element is configured so that a refractive index difference between the two optical materials is smaller for light having a shorter wavelength, and is larger for light having a longer wavelength. In a diffractive optical element described in Japanese Patent Publication No. 09-127321, a combination of such optical materials reduces wavelength dependency of diffraction efficiency.
Although a plurality of optical members are not stacked, a diffractive optical element described in Japanese Patent Publication No. 2009-134223 is a diffractive optical element including at least one element section in which a base section and a diffraction grating are formed on a substrate with a middle layer being interposed between the base section and diffraction grating. The base section and the diffraction grating are made of the same material, and extinction coefficients Ka and Kb for materials of the diffraction grating and the middle layer are properly set.